Mushrooms or macrofungi with distinctive fruiting bodies of sufficient size that can be seen with the naked eye include about 12,000 species of varying degrees of edibility. Approximately 100 species have been tested for cultivation and only 11 to 13 have been cultivated on an industrial scale. The world production of cultivated edible mushrooms in 2002 was estimated to be about 9 million tons and was valued at about ten billion US dollars. The most popular species of cultivated edible mushrooms include Agaricus bisporus (J. Lge) Imbach, Lentinus edodes, Pleurotus spp., Auricularia spp., Volvariella volvacea (Fr.) Singer, Flammulina velutipes (Fr.) Singer, Tremella fuciformis Berk., Hypsizygus marmoreus (Peck) Bigel., Pholiota nameko (T. Ito) S. Ito et Imai, Grifola frondosa (Dicks.: Fr.) S. F. Gray, Hericium erinaceus (Bull.: Fr.) Pers., Dictyophora indusiata (Vent.: Pers.) Fischer, Stropharia rugosoannulata Far. apud Murr., Lepista nuda (Bull.: Fr.) Cooke, and Agrocybe aegerita (Brig.) Sing.
Many mushrooms are now cultivated intensively as opposed to being allowed to grow under reasonably wild conditions.
The cultivation of fruiting bodies of mushrooms deals with living organisms, for example, the mushroom itself and other microorganisms, which may either be harmful or beneficial. Therefore, the methods employed in mushroom cultivation require modifications depending upon the region being cultivated, substrates available, environmental conditions, and species of microorganisms encountered. The cultivation of mushrooms for fruiting body production is a long-term process needing from one to several months for the first fruiting bodies to appear.
The shiitake mushroom [scientific name: Lentinus edodes (Berk.) Singer] is a scented, edible mushroom grown in Asia, largely in Japan, China, and South Korea. It can grow successfully on a wide variety of hardwood tree species. The common name ‘shiitake’ is derived from the Japanese word for the hardwood host tree ‘shii’ and mushroom—‘take’. In China it is called the ‘hsaing ku’ or fragrant mushroom and elsewhere is also known as the Black Forest Mushroom. The shiitake is currently the second most widely cultivated mushroom in the world, serving as both an edible mushroom and more recently for medicinal and health purposes.
Shiitake mushrooms grow on a lignocellulose base as opposed to coprophilous mushrooms, for example, the buttom mushroom (Agaricus bisporus), which grow by decomposing dung or compost. It is very difficult to grow the shiitake mushroom because it grows only on wood, whereas the other mushrooms will grow on almost any sort of cellulose base such as straw or cotton waste. The shiitake mushroom apparently requires lignin as well as cellulose as a base for growth.
In nature, the shiitake fungus propagates and spreads from spores produced by the mushroom. However, for cultivation, spore germination is too unreliable. Instead, logs are inoculated with actively growing fungi. The fungus is first adapted to wood by growing it directly on small pieces of wood. Active fungal cultures, intended as inoculum for mushroom cultivation, are called spawn. Because the quality of the crop can be no better than the spawn, growers must use viable shiitake spawn of a good variety in pure culture, free of weed fungi and bacteria.
Currently, in Japan, the cultivation of shiitake mushrooms is achieved through growing the mycelia of the shiitake spawn on wood fiber chips rather than on logs. The chips are soaked through a distilled water process, and the mushroom beds are sterilized by steam before being inoculated with shiitake spawn. Due to the sensitive nature of the spawn, no pesticides, fungicides or chemicals are added, as they would destroy the mycelium or severely retard its development.
U.S. Pat. No. 1,833,089 discloses a method for culturing mushrooms of various kinds consisting of culturing spawns of mushrooms with a culture media prepared from sawdust and brans, which are kneaded together with water. Said media is heat-sterilized and cooled before the addition of the spawn.
U.S. Pat. No. 4,127,965 discloses a method for cultivating shiitake and other tree mushrooms on a substrate comprised of cellulosic material, preferably in tree log form, and nutrients. In this method, the substrate comprises at least 60% of a cellulosic material, e.g., sawdust obtained from hardwood species, and nutrients consisting of 5-15% starch and 1-15% proteinaceous waste materials. The substrate is introduced into a flexible container, which is sealed and sterilized. After cooling, the substrate is inoculated with the appropriate spawn. The container is sealed against particulate matter, but not against air, and the substrate incubated at moderately elevated temperatures while being molded into a desired form (e.g., log or stump) in the container and is then removed from the container and cured, as required, at moderately reduced temperatures.
U.S. Pat. No. 4,637,163 discloses a method of producing wood-rotting edible mushrooms Lentinus edodes, Kuehneromyces mutabilis, Pholiota spp. and Pleurotus spp. utilizing a bed material mixed from a carbohydrate, lignin and protein-containing compound material and minor amount of peat.
U.S. Pat. No. 4,646,466 describes a substrate for the cultivation of Basidiomycetes Agaricales mushrooms, particularly the gourmet Quebec Pleurotus Super Mushroom, comprised of straw, wood chips from broad-leaved trees, crushed shelled ears of corn, vermiculite, Japanese millet, mixed cereal grains, lime, and micro-cell.
U.S. Pat. No. 4,874,419 describes a non-sterile, pasteurized substrate composition suitable for growing shiitake mushrooms consisting of a nitrogen-containing compost mixture consisting essentially of a vegetative waste, a mineral fertilizer and water, said mixture having a moisture content of about 65% to 80%. The vegetative waste consists essentially of cellulosic and lignin-containing materials such as wheat straw, cottonseed meal, corncobs, and mixtures thereof, and the mineral fertilizer comprises potash, gypsum, and ammonium nitrate as sources of potassium, calcium, and nitrogen, respectively.
Cultivation of shiitake has remained in a primitive state until very recently. Traditionally, shiitake mushrooms have been grown on tree trunks with some types of trees supporting more abundant growth than others. Growth of shiitake on trees typically requires between one and two years until the first crop of fruiting bodies is produced.
It would be very desirable to provide methods for commercial production of shiitake mushrooms of good quality in a relatively short time.